Rare earth tellurites and method of producing same

ABSTRACT

Tellurium compounds having the general formula (AxBy)Te4011 where A and B is a rare earth metal or yttrium, x is from 0 to 2, y is from 0 to 2, and x plus y is 2. Where A and B are the same metal the formula is M2Te4011. The compounds are prepared by reactions between Te02 and the rare earth oxides.

United States Patent 1 1 Redman 14 1 Mar. 27, 1973 I RARE EARTHTELLURITES AND METHOD OF PRODUCING SAME [75] inventor: Michael J.Redman, Belmont, Mass.

[73] Assignee: Kennecott Copper Corporation,

New York, NY.

[22] Filed: Oct. 18, 1971 [21] Appl. No.: 190,267

Related U.S. Application Data [63] Continuation-impart of Ser. No.878,915, Nov. 21,

1969, abandoned.

52 1 us. 01 423/263, 1237368 106/288 B, 252/635, 252/301.4 s

51 1111. C1. ..C22b 59/00 [58] Field 61 Search ..23/50 R, 21, 16, 20;106/288 1; 252/635, 301.4 s

[56] References Cited UNITED STATES PATENTS 3,053,616 9/1962 Bayer..23/50 R Kent et al., Inorganic Chemistry," Vol. I, Nov. 1962, pp.956-958.

Primary Examiner-Herbert T. Carter AttorneyJohn L. Sniado et al.

[57] ABSTRACT Tellurium compounds having the general formula (A B,,)Te,0where A and B is a rare earth metal or yttrium, x is from O to 2, y isfrom 0 to 2, and x plus y is 2. Where A and B are the same metal theformula is M Te O The compounds are prepared by reactions between TeOand the rare earth oxides.

10 Claims, No Drawings RARE EARTH TELLURITES AND METHOD OF PRODUCINGSAME This application is a continuation-in-part of application Ser. No.878,915 filed Nov. 21, 1969 and now abandoned.

BACKGROUND OF THE INVENTION The prior patent art shows a number oftellurite compounds. For example U.S. Pat. No. 3,053,616 disclosestitanium, zirconium and tin tellurites and U.S. Pat. No. 3,053,618teaches the method for making the titanium, zirconium and tintellurites. U.S. Pat. No. 3,053,617 discloses the compound ceriumtellurite and U.S. Pat. No. 3,053,619 teaches the method of producingthe cerium tellurite. Compounds containing hexavalent tellurium aredisclosed in U.S. Pat. Nos. 3,309,168 and 3,309,169.

SUMMARY This invention is directed to new tellurium compounds having thegeneral formula (A,,B,,)Te.,0 where A and B is a rare earth metal oryttrium, x is from to 2, y is from 0 to 2, and x plus y'is 2. Where Aand B are the same rare earth metal or yttrium the formula may be whereM is a rare earth metal or yttrium.

This invention is also directed to a process for preparing the rareearth and yttrium compounds containing tellurium. These compounds areprepared by the solid state reactions between tellurium dioxide and therare earth sesquioxides. These compounds may also be prepared ascrystals from melts containing excess tellurium dioxide above thatneeded for the formation of (A,B,,)Te O and M Te O The new metaltellurites of this invention find application as laser host materials.The dielectric properties of the new tellurites allow them to be used inelectronic components where materials having relatively high dielectricconstants are required. The compounds have very desirable colors and areused as pigments in ceramic glazes, enamels, paints and dyes.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The products of this inventionare compounds of the formula (A,B,,)Te,0, wherein A and B are arareearth metals selected from lanthanum (La), cerium (Ce), praseodymium(Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu),gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium(Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu) or yttrium (Y).

According to the invention the new compounds can be prepared by mixingweighed mixtures of tellurium dioxide and a rare earth oxide, or amixture of rare earth oxides in the ratio of from about 4 molestellurium dioxide to about 1 mole of rare earth oxide, or 1 moleequivalent of mixed rare earth oxides and carrying out a solid-statereaction. The ratios of the oxides should be substantially as stated,but higher ratios can be used. When ratios greater than 4:1 are used thecompounds of this invention are produced in admixture with the excesstellurium dioxide. The reactants are intimately admixed in finelydivided powder form. The intimately admixed powders are compacted into acohesive mass, wrapped in platinum foil to prevent volatilizationlosses, and heated in a non-reducing atmosphere such as air or nitrogen.Temperatures of firing are from about 700 to 1,000 C. Firing time isgenerally from about 5 to 20 hours, preferably 8 to 10 hours, afterwhich the compound is cooled to room temperature.

Single crystals of the new compositions of this invention may beprepared from melts containing about mole percent tellurium dioxide and15 mole percent rare-earth oxide or 15 mole percent equivalent of mixedrare earth oxides or yttrium oxide contained in a tightly coveredplatinum crucible by cooling in air. The melt temperatures ran fromabout 850 to 1,000 C and cooling rates of 220 per hour were employed.Cooling rates up to about C per hour may be used but result in smallercrystals that are difficult to separate from the tellurium dioxidematrix. The crystals were then mechanically separated from thesolidified melt. It is also possible to produce larger crystals byemploying a seeding technique by introducing a seed crystal or aplatinum wire into the melt on which the crystals grow.

EXAMPLE I Preparation of La Te O Twenty mole per cent of La O (0.651 gm)was intimately mixed with 80 mole percent of TeO, l .276 gm) and pressedinto pellet form. The pellets were wrapped in platinum foil and fired ina nitrogen atmosphere at about 800 C for 8 to 10 hours. The reactedoxides were cooled and examined. A white powdered product was obtained.Table 11 below gives the x-ray powder diffraction pattern.

EXAMPLE 11 Preparation of Gd Te O Following the same general procedureas outlined-in Example I, 80 mole percent TeO, (1.276 gm) was reacted inthe solid state with 20 mole percent of 0e 0, (0.725 gm) for about 8hours at 800 C. A white powdered product was obtained after cooling toroom temperature.

EXAMPLE III Preparation of Lu Te O Following the procedures of Examples1 and II, 20 mole percent Lu O (0.796 gm) was reacted with 80 molepercent TeO (1.276 gm) for about 8 hours at 800 C. A white powderedproduct was obtained. The x-ray powder diffraction pattern is given inTable III below.

EXAMPLE IV Preparation of Y Te O Eighty mole percent TeO (1.276 gm) wasreacted in the solid state with 20 mole percent Y O (0.4516 gm) at about800 C for about 8 hours. A white powdered product with a faint yellowishcast was obtained. The product had the unit cell dimensions as shownin'Table I below.

EXAMPLE V Preparation of Single Crystals of La Te O Fifteen mole percentLa O (4,887 gm) was intimately mixed with eighty-five mole percent TeO(13.56 gm) and melted in a platinum crucible in air at about 800 C. Themelt was maintained at 900 C for 2 hours and then cooled at 20 per hourfor 15 hours. The furnace was then shut off and allowed to cool down toroom temperature. Colorless transparent single crystals of La Te O werethen separated from the TeO matrix.

EXAMPLE VI Preparation of Single Crystals of Y Te.,O

Following the procedure of Example V, 12.5 mole percent Y O (2.822 gm)was mixed and melted with 87.5 mole percent TeO (13.96 gm). Colorlesssingle crystals of Y Te,O were found in a matrix of TeO EXAMPLE v11Preparation of Single Crystals ofGd Te O Fifteen mole percent (5.436 gm)Gd o was mixed and melted with 85 mole percent (13.56 gm) TeO inaccordance with the procedure of Example V. Colorless transparentcrystals of Gd Te O were recovered in a matrix of TeO EXAMPLE V111Preparation of Neodymium Substituted La nthanum Tellurite.

1. Eighty-five mole percent TeO (13.56 gm), three mole percent Nd O(1.000 gm) and twelve mole percent La O (3.909 gm) were intimatelymixed, placed in a platinum crucible and heated to 900 C. Uponcontrolled cooling mixed crystals of neodymium substituted lanthanumtellurite was obtained. The crystals were blue in color and transparent.Chemical analysis indicated the crystals contained 4.9 mole percent Nd OThe formula may be represented as (La Nd )Te O where x is 1.51 and y is0.49.

. Following the above procedure, 14 mole percent La O (72.98 gm), 1 molepercent 1911,0 (5.386 gm) and 85 molepercent TeO (217.06 gm) were mixedand melted. A seed crystal of La Te O was introduced from the top andcrystalline material grew on the, seed beginning at temperatures fromabout 765 to 772 C. A light blue mixed single crystal was obtainedcontaining 1.2 mole percent Nc1 corresponding to the formula (La Nd 4 n-The tellurium contents of the compositions were checked by twomethods.Compositions were dissolved in concentrated hydrochloric acid followedby reduction to elemental tellurium with sulfurous acid and subsequentweighing. The second method, based on a method devised by Levin andSwann, Talanta 1 (1958), 276-80, in which iodine, liberated by theoxidation of Te (IV) by iodide ion, is titrated against thiosulfate.

Single crystals of the new compounds of this invention corresponding tothe formula (A.-,B,,),'1e O and M,Te OWere obtained by slow cooling oftellurium dioxide rich melts. The tellurites .of all the rare-earthelements examined gave x-ray powder film patterns and diffractometertraces at room temperatures showdata is given in Table 1 below.

TABLE 1 Unit Cell Dimensions of (A B,,) Te O,

Rare X-Ray earth Volume Density or At. yttrium No. a(A) b(A) c(A) B Ag/cm La 57 12.80 5.278 16.42 105.92 1066.5 6.01 Nd 60 12.60 5.216 16.27106.00 1028.4 6.30 Sm 62 12.56 5.174 16.19 106.00 1011.2 6.48 Eu 6312.50 5.163 16.14 106.02 1001.2 6.57 Gd 64 12.46 5.142 16.09 106.08991.1 6.71 Dy 66 12.40 5.120 16.04 106.08 978.7 6.86 H0 67 12.37 5.10516.00 106.12 971.0 6.95 Y 39 12.37 5.100 15.99 106.12 968.8 5.92 Er 6812.35 5.089 15.97 106.14 964.4 7.03 Tm 69 12.29 5.073 15.94 106.10 955.27.12 Yb 70 12.26 5.069 15.92 106.15 950.6 7.21 Lu 71 12.26 5.058 15.90106.18 946.6 7.27

For the purpose of identification, Tables 11 and 111 show theinterplanar spacings and Miller indices ass1gned to the peaks in theforward-reflection regions of the diffractometer traces of the first andlast members of the rare-earth series. The intensities are listed aspeak he1ghts above background and expressed as percentages of theintensity of the strongest line.

TABLE 11 Indexed X-Ray Powder Diffraction Pattern for LEI T4O1 d) 1 hklTABLE 111 Indexed X-Ray Powder Diffraction Pattern for Lu Te4O11 a A 1hkl Optical and infrared properties of two of the new compounds wereobtained. For La Te O the shortwave absorption edge occurs at 0.325microns; the material is then transparent out to 6 microns where a sharpcutoff occurs. Spectra of the neodymium tellurite show thecharacteristic absorptions of the Nd ion with a shortwave absorptionedge at 0.34 microns and transparency to 6 microns. Dielectric andelectrical resistivity measurements were made on single crystal La TeO.Table IV shows the results for measurements at a frequency of 1kilohertz.

TABLE IV Dielectric Properties of La Te O Even though only rare earthtellurites of the general formulas M,Te O and (A,B,,) Te O have beenprepared, those skilled in the art would observe from the data presentedherein, particularly referring to Table I, that rare earth tellurties ofthe general formula (A,B,CD Te 0 could be prepared. Any mixture of rareearths could be used for the rare earth moiety in preparing thetellurite compound as long as 'mixture of rare earths comprises a totalof about 20 mole percent of the compound. An examination of the data inTable I derived from powder patterns of film and from diffractometertraces shows, from one end of the rare earth series to the other end,i.e., from lanthanum to lutetium, that there is but small differences inthe atomic spacing. Therefore, those skilled in the art would concludethat rare earth tellurites containing a mixture of any of the rareearths could be prepared in accordance with the invention disclosedherein.

EXAMPLE IX Praseodymium substituted EXAMPLE X Preparation of SamariumSubstituted Lanthanum Tellurite Eighty mole percent ofTeO (1.276 gm), 8mole percent of Sm O (0.28 gm) and 12 mole percent of La O (.391 gm) areintimately mixed and pressed into pellet form. The pellets are wrappedin platinum foil and fired in a nitrogen atmosphere at about 800 C for 8to 10 hours. The reacted oxides are cooled and examined. An off white tocream colored powdered product is obtained.

EXAMPLE XI Preparation of Lanthanum Substitute Dysprosium TelluriteEighty mole percent of TeO (1.276 gm), 15 mole percent of Dy O (0.56 gm)and 5 mole percent of La o (0.16 gm) are intimately mixed and pressedinto pellet form. The pellets are wrapped in platinum foil and fired ina nitrogen atmosphere at about 900 C for 10 to 12 hours. The reactedoxides are cooled and examined. A white powdered product is obtained.

EXAMPLE XII Preparation of Europium Substituted Lanthanum TelluriteEighty-five mole percent of TeO (13.56 gm), 12 mole percent of La O(3.91 gm) and 3 mole percent of Eu O (1.16 gm) are intimately mixed,placed in a platinum crucible and heated to about l,000 C. Uponcontrolled cooling mixed light pink crystals of europium substitutedlanthanum tellurite are obtained. Chemical analysis will show crystalscontaining about 3.8 mole percent Eu O The formula may be represented as(La Eu Te O where x is 1.62 and y is 0.38.

EXAMPLE XIII Preparation of Lanthanum Substituted Lutetium TelluriteEighty-five mole percent of TeO (13.56), 12 mole percent of 1311,0 (4.77gm) and 3 mole percent of La,0 (0.975 gm) are intimately mixed, placedin a platinum crucible and heated to about 950 C. Upon controlledcooling mixed colorless crystals of lanthanum substituted lutetiumtellurite are obtained. Chemical analysis will show crystals containingabout 3.9 mole percent Lu O The formula may be represented as (Lu,La,,)Te O where x is 1.61 and y is 0.39.

EXAMPLE XIV Preparation of Neodymium substituted Praseodymium TelluriteEighty mole percent of TeO (1.276 gm), 15 mole percent of Pr O (0.496gm) and 5 mole percent of Nd O (0.17 gm) are intimately mixed andpressed into pellet form. The pellets are wrapped in platinum foil andfired in a nitrogen atmosphere at about 925 C for 8 to hours. Thereacted oxides are cooled and examined. A greenish blue powdered productis obtained.

EXAMPLE XV Preparation of Praseodymium substituted Europium TelluriteEighty mole percent of TeO (1.276 gm), 14 mole percent of Eu O '(.49 gm)and 6 mole percent of Pr O (0.19 gm) are intimately mixed and pressedinto pellet form. The pellets are wrapped in platinum foil and fired ina nitrogen atmosphere at about 850 C for 6 to 9 hours. The reactedoxides are cooled and examined. A light yellow powdered product isobtained.

EXAMPLE XVI Preparation of Dysprosium Substituted Praseodymium TelluriteEighty mole percent of TeO 1.27 gm), 13 mole percent of Pr O (0.428 gm)and 7 mole percent of Dy O (0.26 gm) are intimately mixed and pressedinto pellet form. The pellets are wrapped in platinum foil and tired ina nitrogen atmosphere at about 800 C for 8 to 10 hours. The reactedoxides are cooled and examined. A yellow green powdered product isobtained.

EXAMPLE XVII Preparation of Praseodymium Substituted Thulium TelluriteEighty-five mole percent of TeO, (13.56 gm), 14 mole percent of Tm o(5.40 gm) and 1 mole percent of Pr O (.38 gm) are intimately mixed,placed in a platinum crucible and heated to about 900 C. Upon controlledcooling mixed off white crystals of praseodymium substituted thuliumtellurite are obtained. Chemical analysis will show crystals containingabout 1.4 mole percent Pr O The formula may be represented as (Tm Pr TeO where x is 1.86 and y is 0.14.

EXAMPLE XVIII Preparation of Yttrium Substituted Praseodymium TelluriteEighty-five mole percent of TeO (13.56 gm), and 3 mole percent of Y,O(0.67 gm) and 12 mole percent Pr,O (3.95 gm) are intimately mixed,placed in a platinum crucible and heated to about 900 C. Upon controlledcooling mixed green colored crystals of yttrium substituted praseodymiumtellurite is obtained. Chemical analysis will show crystals containingabout 3.6 mole percent Y 0 The formula may be represented as (Pr, .Y,,)Te O where x is 1.64 and y is 0.36.

EXAMPLE XIX Preparation of Neodymium Substituted Samarium TelluriteEighty mole percent of TeO (1.276 gm), 15 mole percent of Sm O (0.52 gm)and 5 mole percent of Nd o (.17 gm) are intimately mixed and pressedinto pellet form. The pellets are wrapped in platinum foil and fired ina nitrogen atmosphere at about 900 C for 8 to 10 hours. The reactedoxides are cooled and examined. A light blue powdered product isobtained.

EXAMPLE XX EXAMPLE XXI Preparation of Holmium Substituted NeodymiumTellurite Eighty mol percent of TeO (1.276 gm), 15 mole percent of Nd O(0.50 gm) and 5 mole percent of H0 0 (0.19 gm) are intimately mixed andpressed into pellet form. The pellets are wrapped in platinum foil andfired in a nitrogen atmosphere at about 900 C for 10 to 12 hours. Thereacted oxides are cooled and examined. A light blue powdered product isobtained.

EXAMPLE XXII Preparation of Ytterbium Substituted Neodymium TelluriteEighty mole percent of TeO (1.276 gm), 12 mole percent of M 0. (0.40 gm)and 8 mole percent of Yb O (0.31 gm) are intimately mixed and pressedinto pellet form. The pellets are wrapped in platinum foil and fired ina nitrogen atmosphere at about 800 C for 12 to 14 hours. The reactedoxides are cooled and examined. A blue powdered product is obtained.

EXAMPLE XXIII Preparation of Europium Substituted Samarium TelluriteEighty-five mole percent of TeO, (13.56 gm), 12 mole percent of Sm O(4.2 gm) and 3 mole percent of Eu O (1.05 gm) are intimately mixed,placed in a platinum crucible andheated to about 950 C. Upon controlledcooling very pale pink colored mixed crystals of europium substitutedsamarium tellurite are obtained. Chemical analysis will show crystalscontaining about 3.5 mole percent B11 0 TI-Ie formula may be representedas (sm Eu Te O where x is 1.65 and y is 0.35.

EXAMPLE XXIV Preparation of Dysprosium Substituted Samarium TelluriteEighty-five mole percent of TeO (13.56 gm), 10 mole percent of Sm O(3.48 gm) and 5 mole percent of Dy O (1.86 gm) are intimately mixed,placed in a platinum crucible and heated to about 900 C. Upon controlledcooling cream to light yellow colored mixed crystals of dysprosiumsubstituted samarium tellurite are obtained. Chemical analysis will showcrystals containing about 6 mole percent Dy O The formula may berepresented as (Sm Dy Te O where x is 1.4 and y is 0.6.

EXAMPLE XXV Preparation of Samarium Substituted Thulium Tellurite Eightymole percent of TeO (1.276 gm), 15 mole percent of Tm O (0.58 gin) and 5mole percent of Sm O (.17 gm) are intimately mixed and pressed intopellet form. The pellets are wrapped in platinum foil and fired in anitrogen atmosphere at about 850 C for 12 to 14 hours. The reactedoxides are cooled and examined. An off white powdered product isobtained.

EXAMPLE XXVI EXAMPLE XXVII Preparation of Gadolinium SubstitutedEuropium Tellurite Eighty-five mole percent of Te (13.56 gm), 11'

mole percent of Eu o (3 .87 gm) and 4 mole percent of Gd o (1.45 gm) areintimately mixed, placed in a platinum crucible and heated to about1,000 C. Upon controlled cooling pale pinkish white mixed crystals ofgadolinium substituted 'europium tellurite are obtained. Chemicalanalysis will show crystals containing-about mole percent Gd o Theformula may be represented as (Eu Gd Te O where x is 1.5 and y is 0.5.

EXAMPLE XXVlll Preparation of Europium Substituted Holmium TelluriteEighty mole percent of TeO (1.276 gm), 18 mole percent of H0 0 (0.68 gm)and 2 mole percent .of Eu O (0.07 .gm)-are intimately mixed and pressedinto pellet form. The pellets are wrapped in platinum foil and fired inanitrogen atmosphere at about 850C for i to 12 hours. The reacted oxidesare cooled .and examined. A light pinkish powdered product isobtained.

EXAMPLE XXIX Preparation of Ytterbium Substituted Europium TelluriteEighty mole percent of TeO (1.276 gm), 12 mole percent of Eu O (0.42 gm)and 8 mole percent of Yb O (0.31 gm) are intimately mixed and pressedinto pellet form. The pellets are wrapped in platinum foil and fired ina nitrogen atmosphere at about 800 C for 6 to 7 hours. The reactedoxides are cooled and examined. A pale reddish pink powdered product isobtained.

EXAMPLE XXX Preparation of Dysprosium Substituted Gadolinium TelluriteEighty mole percent of TeO 1.27 gm), 15 mole percent of Gd- O (0.54 gm)and 5 mole percent of Dy O (0.18 gm) are intimately mixed and pressedinto pellet form. The pellets are wrapped in platinum foil and fired ina nitrogen atmosphere at about 900 C for 8 to 12 hours. The reactedoxides are cooled and examined. A light yellow powdered product isobtained.

EXAMPLE XXXI Preparation of Erbium Substituted Gadolinium TelluriteEight-five mole percent ofTeO (13.56 gm), 12 mole percent of Gd O (4.35gm) and 3 mole percent of Er o (1.15 gm) are intimately mixed, placed ina platinum crucible and heated to about 900 C. Upon controlled coolingpinkish white mixed crystals of erbium substituted gadolinium telluriteare obtained. Chemical analysis will show crystals containing about 4mole percent Er O The formula may be represented as (Gd,Er,,) Te.,0where x is 1.6 and y is 0.4.

EXAMPLE xxxn Preparation of Lutetium Substituted Gadolinium TelluriteEighty-five mole percent of-Te0 (13.56 gm), 10 mole percent of Gd O(3.62 gm) and 5 mole percent of [M 0 (1.99 gm) are intimately mixed,placed in a platinum crucible and heated to about 900 C. Upon controlledcooling off white mixed crystals of lutetium substituted gadoliniumtellurite are obtained. Chemical analysis will show crystals containingabout 5.5 mole percent 1.11.0 The formula may be represented as (Gd,.Lu,,) Te O where x is 1.45 and y is 0.55.

EXAMPLE XXXIII Preparation of Holmium Substituted Dysprosium TelluriteEighty-five mole percent of TeO (13.56 gm), 12

.mole percent of Dy O (4.47 gm) and .3 mole percent of H0 0 (1.13 gm)are intimately mixed, placed in a platinum crucible and heated to about900 C. Upon controlledcoolinglightyellow mixed crystals of holmitumsubstituted dysprosium tellurite are obtained. Chemical analysis willshow crystals containing about 4 mole percent H0 0 The formula'may berepresented as-.(Dy,,I-1o,,)Te O where x is 1.6 and y is 0.4.

EXAMPLEXXXIV Preparation of Ytterbium Substituted Dysprosium TelluriteEighty mole percent of TeO (1.276 gm), 14 mole percent of Dy O (0.52 gm)and 6 mole percent of Yb O (0.24 gm) are intimately mixed and pressedinto pellet form. The pellets are wrapped in platinum foil and fired ina nitrogen atmosphere at about 1,000 C for 8 to 12 hours. The reactedoxides are cooled and examined. A white powdered product is obtained.

EXAMPLE XXXV Preparation of Erbium Substituted Holmium Tellurite Eightymole percent of TeO (1.276 gm), 15 mole percent of H 0,, (0.57 gm) andmole percent of Er O (0.19 gm) are intimately mixed and pressed intopellet form. The pellets are wrapped in platinum foil and fired in anitrogen atmosphere at about 850 C for 8 to hours. THe reacted oxidesare cooled and examined. A light yellow powdered product is obtained.

EXAMPLE XXXVI Preparation of Lutetium Substituted Holmium TelluriteEighty-five mole percent ofTeO 13.56 gm), 8 mole percent of H0 0 (3.02gm) and 7 mole percent of Lu O (2.78 gm) are intimately mixed, placed ina platinum crucible and heated to about 850 C. Upon controlled coolingwhite to pale yellow mixed crystals of lutelium substituted holmiumtellurite are obtained. Chemical analysis will show crystals containingabout 10 mole percent Lu O The formula may be represented as (Ho,Lu,,)Te O where x is l and y is 1.

EXAMPLE XXXVll Preparation of Thulium Substituted Erbium TelluriteEighty-five. mole percent of TeO (13.56 gm), 10 mole percent of Er O(3.82 gm).and 5 mole percent of Tm o (1.93 gm) are intimately mixed,placed in a platinum crucibleand heated to about 850 C. Upon controlledcooling pale pink mixed crystals of thulium substituted erbium telluriteare obtained. Chemical analysis will show crystals containing about 6mole percent Tm O The formula may be represented as (Er T- m Te O wherex is 1.2 and y is 0.6.

EXAMPLE XXXVI" Preparation of Erbium Substituted Yttrium TelluriteEighty mole percent of TeO (1.276 gm), 17 mole percent of Y,O;, (0.38gm) and 3 mole percent of Er- O (0.1 1 gm) are intimately mixed andpressed into pellet form. The pellets are wrapped in platinum foil andfired in a nitrogen atmosphere at about 900 C for 10 to 12 hours. Thereacted oxides are cooled and examined. A yellowish white powderedproduct is obtained.

EXAMPLE XXXlX Preparation of Ytterbium Substituted Thulium Tellurite aEighty mole percent of TeO, (1.276 gm), 15 mole percent of Tm O (0.58gm) and 5 mole percent of Yb,O (0.20 gm). are intimately mixed andpressed into pellet form. The pellets are wrapped in platinum foil andfired in a nitrogen atmosphere at about 900 C for 8 to 10 hours..Thereacted oxides are cooled and examined. A white powdered product isobtained.

EXAMPLE XL Preparation of lutetium substituted Ytterbium TelluriteEighty-five mole percent of TeO (13.56 gm), 10 mole percent of Yb O (3.9gm) and 5 mole percent of Lu O (1.98 gm) are intimately mixed, placed ina platinum crucible and heated to about 1,000 C. Upon controlled coolingwhite mixed crystals of lutetium substituted ytterbium tellurite areobtained. Chemical analysis will show crystals containing about 6 molepercent Lu,o,. The formula may be represented as (Yb,Lu,,)Te O where xis 1.4 andy is 0.6.

EXAMPLE XLl Preparation of Lutetium Substituted Yttrium Tellurite IEighty-five mole percent of TeO (13.56 gm), 12 mole percent of Y O (2.70gm) and 3 mole percent of Lu O (1.19 gm) are intimately mixed, placed ina platinum crucible and heated to about 800 C. Upon controlled coolingyellowish-white mixed crystals of lutetium substituted yttrium telluriteare obtained. Chemical analysis will show crystals containing about 3.8mole percent 1.11 0,. The formula may be represented as (Y Lu,,) Te.,0where x is 1.62 and y is 0.38.

What 1 claim is:

1. A new composition of matter having the formula where A and B are arare earth metal or yttrium, x is from 0 to 2, y is from 0 to 2 and xplus y is 2.

2. The composition of claim 1 wherein A and B are selected from thegroup of lanthanum, neodymium,

samarium, veuropium, gadolinium, dysprosium, holmium, erbium, thulium,ytterbium, lutetium, and yttrium.

3. A new composition of matter having the formula MzTego where M is arare earth metal or yttrium.

4. The composition of claim 3 wherein M is selected from lanthanum,neodymium, samarium, europium, gadolinium, dysprosium, holmium, erbium,thulium, ytterbium, lutetium, and yttrium.

5. The composition of claim 3 wherein M is a mixture of rare earthmetals.

6. The method of making the compound M Te O where M is selected fromlanthanum, neodymium, samarium, europium, gadolinium, dysprosium,holmium, erbium, thulium, ytterbium, lutetium, and yttrium by thesolid-state reaction which comprises intimately mixing powders of M 0and TeO in a molar ratio of TeO to M 0 of at least 4:1, compressing theadmixture into a cohesive mass, .heating in a non-reducing atmosphere ata temperature at least from about 700 C up to the temperature at whichthe compound begins to decompose, cooling to room temperature andrecovering M2T640.

7. The method of claim 6 wherein M is a mixture of rare earth metals.

lanthanum,

more than C per hour and separating the crystals of M Te O from thematrix.

9. The method of claim 8 wherein a seed crystal is introduced into themelt on which the crystal grows.

10. The method of claim 8 wherein M is a mixture of rare earth metals.

2. The composition of claim 1 wherein A and B are selected from thegroup of lanthanum, neodymium, samarium, europium, gadolinium,dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and yttrium.3. A new composition of matter having the formula M2Te4O11 where M is arare earth metal or yttrium.
 4. The composition of claim 3 wherein M isselected from lanthanum, neodymium, samarium, europium, gadolinium,dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and yttrium.5. The composition of claim 3 wherein M is a mixture of rare earthmetals.
 6. The method of making the compound M2Te4O11, where M isselected from lanthanum, neodymium, samarium, europium, gadolinium,dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and yttriumby the solid-state reaction which comprises intimately mixing powders ofM2O3 and TeO2 in a molar ratio of TeO2 to M2O3 of at least 4:1,compressing the admixture into a cohesive mass, heating in anon-reducing atmosphere at a temperature at least from about 700* C upto the temperature at which the compound begins to decompose, cooling toroom temperature and recovering M2Te4O11.
 7. The method of claim 6wherein M is a mixture of rare earth metals.
 8. The method of makingsingle crystals having the general formula M2Te4O11 where M is selectedfrom lanthanum, neodymium, samarium, europium, gadolinium, dysprosium,holmium, erbium, thulium, ytterbium, lutetium, and yttrium comprisingintimately mixing M2O3 with an excess of TeO2, heating the mixture toits melting point, slowly cooling the melt at no more than 100* C perhour and separating the crystals of M2Te4O11 from the matrix.
 9. Themethod of claim 8 wherein a seed crystal is introduced into the melt onwhich the crystal grows.
 10. The method of claim 8 wherein M is amixture of rare earth metals.